The disclosure of Japanese Patent Application No. 2000-108201 filed on Apr. 10, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an internal combustion engine provided with an electromagnetic valve drive mechanism for causing an exhaust valve to open and close by using electromagnetic force, and a method for controlling the same.
2. Description of Related Art
In recent years, in an internal combustion engine mounted in an automobile or the like, an electromagnetic valve drive mechanism that is capable of arbitrarily controlling the open and close timing of intake and exhaust valves has been developed for the purpose of preventing mechanical loss, due to opening and closing of the intake and exhaust valves while reducing intake pumping loss, and improving net thermal efficiency.
For example, an electromagnetic valve drive mechanism that has an armature, valve-closing electromagnet, valve-opening electromagnet, valve-closing return spring, valve-opening return spring has been proposed. The armature is formed from a magnetic body, and operates to advance and retract in conjunction with the intake and exhaust valves. The valve-closing electromagnet generates an electromagnetic force, in response to a magnetizing current, that displaces the armature in the valve-closing direction. Moreover, the valve-opening electromagnet generates an electromagnetic force, in response to a magnetizing current, that displaces the armature to the valve-opening direction. Finally, the valve-closing return spring retracts the armature to the valve-closing direction, while the valve-opening return spring projects the armature to the valve-opening direction.
Such an electromagnetic valve drive mechanism eliminates the need to mechanically control intake and exhaust valves to open and close using the rotation force of an engine output shaft, i.e., crankshaft, as in a conventional valve train. Therefore, mechanical loss due to mechanically driving the intake and exhaust valves is prevented.
Moreover, the aforementioned electromagnetic valve drive mechanism can independently control the intake and exhaust valves to open and close without the rotation of the engine output shaft. This configuration is advantageous in various respects, such as an increased ability to control the open and close timing, as well as the amount the intake and exhaust valves open.
On the other hand, a vehicle provided with an internal combustion engine having the electromagnetic valve drive mechanism can also include various other electrical equipment, such as spark plugs, fuel injection valves, air-conditioner and headlights. This electrical equipment is powered by the battery and generator that are mounted in the vehicle.
In order to avoid increasing the capacity of the battery and generator, an electromagnetic valve drive circuit, as described in Japanese Patent Laid-Open Publication No. HIE 10-131726, has been proposed. The electromagnetic valve drive circuit described in this publication has a permanent magnet, drive coil, switching portion, and condenser. The permanent magnet is integrally attached to the intake and exhaust valves, and the drive coil generates a magnetic pole that displaces the permanent magnet. The switching portion switches the direction of a magnetizing current applied to the drive coil, and also acts to start and discontinue supply of the magnetizing current to the drive coil. The condenser stores electromotive force induced in the drive coil by inertial movement of the permanent magnet.
This electromagnetic valve drive circuit uses both the electromotive force induced in the drive coil, and the inductance of the drive coil to cause the switching portion to act as a booster switching regulator. This function increases the amount of power regeneratively charged in the condenser. As a result, the amount of power that can be supplied from the condenser to the drive coil is also increased. Accordingly, the amount of power supplied from the outside to the electromagnetic valve drive circuit, i.e., power consumption of the electromagnetic drive circuit, is reduced.
In the aforementioned technology, the power regeneratively charged in the condenser is extremely small as compared to the driving power of the electromagnetic valve drive mechanism. Therefore, when the power required to drive the electromagnetic valve drive mechanism is increased, e.g., when the operating state of the internal combustion engine is operating in a high revolution region, or depending on the operating state of the electrical equipment, other than the electromagnetic valve drive mechanism, it may be impossible to supply the desired driving power to the electromagnetic valve drive mechanism even by using the power of the condenser in addition to the power of both the battery and generator. In such a case, it may be difficult to control the intake and exhaust valves to open and close normally.
For example, when the operating state of the internal combustion engine is operating in the high revolution region, the number of times the intake and exhaust valves open and close per unit time is increased. Therefore, the power required to drive the electromagnetic valve drive mechanism is increased in demand. In addition, the number of times the spark plug and fuel injection valve are actuated per unit time is also increased, along with an increase in the power consumption of the spark plug and fuel injection valve. As a result, the amount of power that can be supplied to the electromagnetic valve drive mechanism is reduced.
In particular, if the electric equipment such as air-conditioner and headlight are operating while the operating state of the internal combustion engine is operating in the high revolution region, the amount of power that can be supplied to the electromagnetic valve drive mechanism is further reduced. Therefore, it may be more difficult to ensure that the required power of the electromagnetic valve drive mechanism is provided.
Moreover, the electromagnetic valve drive mechanism is connected through wire harness to the battery, generator and the like. Therefore, when the operating state of the internal combustion engine is operating in the high revolution region, the amount of current flowing through the wire harness per unit time may increase and exceed a capacity of the wire harness. In this example, it is difficult to supply a desired amount of current to the electromagnetic valve drive mechanism, which can cause the intake and exhaust valves to not open and close normally.
To solve this problem, it is possible to increase the cross-sectional area of the wire harness so as to increase the capacity of current per unit time of the wire harness. However, if the cross-sectional area of the wire harness is excessively increased, the space occupied by the electromagnetic valve drive mechanism, including the wire harness, is subsequently increased, which can make it difficult to mount the electromagnetic valve drive mechanism to the vehicle.
It is an object of the invention to improve reliability of the open/close operation of an exhaust valve by an electromagnetic valve drive mechanism, by providing technology capable of reducing the power required to drive the electromagnetic valve drive mechanism in an internal combustion engine having an electromagnetic valve.
An internal combustion engine having an electromagnetic valve of the invention is provided with a controller for changing an open timing of an exhaust valve so as to reduce power consumption of an electromagnetic valve drive mechanism at a predetermined time. The electromagnetic valve drive mechanism controls the exhaust valve of the internal combustion engine to open and close by using electromagnetic force generated in response to application of a magnetizing current.
Accordingly, in an internal combustion engine having the electromagnetic valve, the controller changes, under predetermined conditions, the open timing of the exhaust valve so as to reduce power consumption of the electromagnetic valve drive mechanism.
In this case, power consumption of the electromagnetic valve drive mechanism under the predetermined conditions is reduced. In other words, the electromagnetic valve drive mechanism controls the exhaust valve to open and close with relatively small power consumption.
As a result, reliability of the open and close operation of the exhaust valve is improved even when the amount of power that can be supplied to the electromagnetic valve train is reduced.